In "That Darn Katz!", after the stop of the Earth's rotation, Big Ben was pulled to Paris, France, replacing the Eiffel Tower. After the original Big Ben was stolen by the supervillain governor, the English must've made a replica.

It is possible that the United Kingdom itself no longer exists as a nation state. This is supported by the fact they are represented in the United Nations as 'Great Britain' and the monarch now uses the title the 'Queen of England'.